The University of Minnesota Duluth’s Natural Resources Research Institute (NRRI) is helping introduce high pressure grinding roll (HPGR) technology to Minnesota’s Iron Range.

Working with Weir Minerals, NRRI acquired an industrial-scale Enduron® HPGR to carry out testing on a variety of ores with this process. This is the only large scale HPGR dedicated to research in the US, NRRI claims.

The NRRI explained: “Traditional taconite pellet-making processes use a rod mill to get the rock to the consistency of coarse sand, and a ball mill to grind the rock into a fine powder. This technology is still in use on Minnesota’s Iron Range by some facilities.

“A taconite plant may have as many as 18 rod mills with one rod alone weighing as much as 500 Ib (227 kg). Tumbling around in the mills with the hard taconite wears away the rods and balls and need to be replaced frequently.”

This is a costly and energy-intensive process and the waste rods and balls are a disposal problem, according to NRRI.

NRRI researchers think there’s a better and more efficient way of carrying out this grinding process with the use of HPGRs.

Tim Lundquist, Weir HPGR Manager for North America, said: “NRRI has done a lot of testing for many of our projects. The proximity to the Iron Range is key, but we’ll also bring in material from all over the US, Canada, and elsewhere when it makes sense. Our preference is to work with NRRI whenever possible due to their flexibility, expediency and expertise.”

Unlike rod or ball mills, HPGRs reduce particles by compressing and crushing the feed between two counter rotating, parallel rollers with a small gap between them. This forces the rocks against each other. There are no rods or balls that need replacing and it reduces energy consumption by about 40% for certain ore types, Breneman said. It also substantially reduces water consumption compared with rod and ball mills.

Reducing energy, eliminating costly grinding media, and higher machine availability will make the Minnesota iron industry more cost competitive while also offering the opportunity to reduce greenhouse gas generation, NRRI said.

NRRI Metallurgical Engineer, Shashi Rao, Lead Researcher on HPGR-related projects at NRRI Coleraine, said: “It’s really helpful to the industry to have their ores tested in our large HPGR before replacing their rod or ball mills.

“We’re able to determine if the ore is amenable to high pressure roll crushing, identify the mineral composition, and test a variety of pressures and roll speeds. Third-party testing is very important.”

Keeping the project moving ahead during the COVID-19 pandemic required extra steps and protocols, according to NRRI. This work was coordinated by NRRI Project Engineer, Jeff Kinkel.

“The machine is isolated to one specific area,” Kinkel said. “We adhered to strict sanitation and masking requirements and communicated daily with the contractor doing the installation.”

NRRI acquired the HPGR technology via Weir Minerals from the shuttered Magnetation LLC operation and both organisations are sharing the cost of maintenance.

“This is a great example of a partnership project,” Kevin Kangas, NRRI Coleraine Director, said. “We’ve been working on this for over two years and it’s exciting to have the global interest in this capability.”

The process is now in place at a Minnesota Iron Range facility with a Weir Minerals Enduron HPGR.

On average, 53% of a mine site’s energy consumption is attributed to crushing and grinding ores, accounting for almost 10% of a site’s production costs, according to information from Weir Minerals. NRRI’s HPGR is manufactured in the Netherlands by Weir Minerals.